A press brake executes a bending process on the basis of cooperation between a punch and a die. A ram is vertically moved using a hydraulic cylinder which is operated by a bidirectional fluid pump. A hydraulic circuit provided in the hydraulic cylinder is shown and described with respect to FIG. 1.
In the hydraulic circuit mentioned above, pipings 101 and 103, connected to an upper cylinder chamber or a lower cylinder chamber of, a hydraulic cylinder (not shown), are connected to a bidirectional fluid pump 107 that is rotated by a servo motor 105. Further, the pipings 101 and 103 are respectively connected to an oil tank 113 via check valves 109 and 111.
Accordingly, the bidirectional fluid pump 107 is rotated by the servo motor 105, a working fluid is supplied to the upper or lower cylinder chamber (not shown) through the piping 101 or the piping 103, and a ram (not shown) is thereby vertically moved. The working fluid is supplied from the oil tank 113 via the check valve 109 or the check valve 111.
For the hydraulic circuit mentioned above, a command is given to the servo motor 105 to rotate the bidirectional fluid pump 107 so that the ram is vertically moved according to a pattern shown in FIG. 2. That is, the ram increases speed according to a fixed acceleration rate, moves at a fixed speed after reaching a predetermined speed, and reduces speed according to a fixed deceleration rate.
However, in the prior art mentioned above, a negative pressure may be applied to a check valve 109 or 111 when the check valve 109 or 111 is still open and the bidirectional fluid pump 107 is reverse rotated to change the moving direction of the ram. When the bidirectional fluid pump 107 is reverse rotated and a positive pressure is suddenly applied, the working fluid may flow back until the open check valve 109 or 111 is closed. When the working fluid flows back, a response is deteriorated, and the movement of the ram is unstable as shown in FIG. 3. Furthermore, a large shock occurs at a time of reverse rotation. Moreover, it is impossible to increase a motion gain of the ram. Accordingly, productivity is reduced.
The present invention takes the problems in the prior art into consideration.
Accordingly, an object of the present invention is to provide a press brake and a method of controlling a bidirectional fluid pump of the press brake. According to an aspect of the present invention, a motion gain of a ram can increase so as to improve productivity by reducing a shock at a time of reverse rotation.
Another object of the present invention is to provide a press brake which can reduce a noise generated by a bidirectional fluid pump that operates a hydraulic cylinder.